Taurochenodeoxycholic acid inhibits intestinal epithelial cell proliferation and induces apoptosis independent of the farnesoid X receptor

Bile acids, such as taurochenodeoxycholic acid (TCDCA), are considered as functional small molecules involved in nutrition regulation or acting with adjuvant therapeutic effects against metabolic or immune diseases. The homeostasis of the intestinal epithelium depends on the conventional cellular proliferation and apoptosis of cells. Herein, mice and normal intestinal epithelial cells (IPEC-J2, a widely used normal intestinal epithelial cell line derived from porcine) were used as models to explore the regulatory effect of TCDCA on the proliferation of intestinal epithelial cells (IECs). In the mouse study, the oral gavage of TCDCA led to a significant reduction in weight gain, small intestinal weight, and the villus height of the intestinal epithelium while inhibiting the gene expression of Ki-67 in the intestinal epithelial crypts of mice (P < 0.05). TCDCA significantly downregulated the expression of the farnesoid X receptor (FXR) and upregulated the expression of caspase-9 in the jejunum (P < 0.05). The results of real-time quantitative PCR (RT-qPCR) suggested that TCDCA significantly inhibited the expression of tight junction proteins zonula occludens (ZO)-1, occludin, claudin-1, and mucin-2 (P < 0.05). In terms of apoptosis-related genes, TCDCA significantly inhibited the expression of Bcl2 and increased the expression of caspase-9 (P < 0.05). At the protein level, TCDCA decreased the expression of Ki-67 and PCNA, as well as FXR (P < 0.05). Caspase inhibitor Q-VD-OPh and guggulsterone, an FXR antagonist, significantly improved the inhibition of TCDCA-induced cell proliferation. Moreover, guggulsterone enhanced TCDCA-induced cell late apoptosis through flow cytometry and significantly lowered the TCDCA-induced up-regulated gene expression of caspase 9, despite both TCDCA and guggulsterone down-regulating the expression of FXR (P < 0.05). Overall, the effect of TCDCA on the induction of apoptosis is not dependent on FXR, whereas it would function via the activation of the caspase system. This provides a new perspective for the application of TCDCA or bile acid as functional small molecules in food, additives, and medicine.